It is widely known that electronic parts such as semiconductor packages generate heat in use, thereby lowering the performance thereof. To solve this problem, various heat dissipating techniques have been used. One typical method is to provide a cooling member such as a heat spreader in the vicinity of a heat-generating part and bring them into close contact to effectively remove heat through the cooling member.
In this case, if there is a space between the heat-generating member and the cooling member, thermal conduction does not proceed smoothly because of the presence of air, which is poor in heat conductivity, and therefore, the temperature of the heat-generating member cannot be sufficiently reduced. To prevent such phenomena, there have been conventionally used, for the purpose of preventing the presence of air, heat-dissipating greases or heat-dissipating sheets that have good heat conductivity and followability to the surface of the member (Patent Literatures 1 to 11).
A thin and compressible heat-dissipating grease is suitable for measures against heat of semiconductor packages in view of heat-dissipating performance. Particularly, it is preferable, in view of reliability, to use a thermosetting heat-dissipating grease that hardly causes outflow of the grease (pumping out) due to the thermal history between heating and cooling of the heat-generating part. In general, a thermosetting heat-dissipating grease contains a reaction retarder in many cases, so that the grease is not cured for a certain time at room temperature even after applied to a heat-generating part. Accordingly, even if a certain time passes after the heat-dissipating grease is applied, the heat-dissipating grease can be compressed and thermally cured into a desired thickness after a cooling member such as a heat spreader is placed thereon, and thus, good crushability can be achieved.
On the other hand, semiconductor packages progress toward miniaturization in recent years, and along with this current, application to finer pattern and less application amount are required in heat-dissipating greases. In these cases, the reaction retarder tends to volatilize due to the increase in surface area of the applied heat-dissipating grease or other factors, which leads to acceleration of the curing reaction. Therefore, the heat-dissipating grease cannot be compressed into a desired thickness when the heat-dissipating grease is thermally cured after a cooling member such as a heat spreader is placed thereon, that is, resulting poor crushability. In addition, the applied heat-dissipating grease cannot sufficiently spread over the whole heat-generating part. Thus, there is a problem of insufficient heat-dissipating performance.